The present invention relates in general to water purification methods and apparatuses, and in particular to a new and useful apparatus and method for treating water by removing sediment and/or treating marine organisms such is, but not limited, to zebra mussels and other marine pests, from ballast water before it is pumped into the ballast of a ship, barge or other sea-going vessel.
Although not native to U.S. or Canadian waters, it is believed that the zebra mussel was transported to North America from Europe in the form of larvae in a ship""s ballast water. They now pose a significant threat to marine equipment and ecology.
Zebra mussels have been identified in the lower tidal reaches of the St. Lawrence River as well as in fresh water environments such as the Great Lakes. It has been observed that eventual colonization into estuarine and coastal areas of North America is inevitable. Zebra mussels also can move around. Smaller ones tend to move more than large ones. Also, mussels that have been torn loose during storms seem to have no trouble re-attaching in new places. They secrete proteinaceous adhesive byssal threads from a gland in the foot known as the byssal gland and use this to firmly attach themselves to solid man-made and natural objects.
Efforts are needed to avoid further spread of these and other non-indigenous marine organism. Zebra mussels, for example, kill all the other unionids (native North American bivalves) and their largest immediate adverse effect is mussel biofouling, or the build-up of zebra mussels on any surface. When water fowl eat zebra mussels the result is elevated levels of contaminants in the birds which lead to reproductive problems.
Predation due to waterfowl could control the populations, however, predation would be limited to the warmer months when the Great Lakes are not frozen over, plus the birds would continue to have reproductive problems. Usually in power and water plants, chemical treatments such as chlorine have been used, however, there are environmental problems associated with this since high levels can produce carcinogenic organic side products. High temperature recirculated water also controls these mussels e.g. in a power plant, but this solution is not always workable or environmentally sound.
See the June, 1996 issue of American Zoologist, for more through discussion of zebra mussels and the problems they cause.
As presented in the National Academy Press publication, STEMMING THE TIDE, Controlling Introductions of Nonindigenous Species by Ships"" Ballast Water, xe2x80x9cThe overall diversity of biota found in ship""s ballast water and the complexity of ballasting patterns and operations mean that predicting the presence of a particular unwanted species in any one vessel is a scientific challenge. Similarly, the great diversity of the larval or juvenile stages of marine invertebrates and fish in ballast water, many of which are not identifiable, means that certifying a vessel as free or safe from all unwanted species is not possible. A further complication is that many of the most prominent introductions of recent years were not recognized as problem species in their donor regions. Ballast water is carried by many types of vessels and is held in a variety of tanks or holds. The relative complexity of ballast operations depends on the size, configuration, and requirements of the ship and on the complexity of its pumping and piping systems. Ballast capacity can range from several cubic meters in sailing boats and fishing boats to hundreds of thousands of cubic meters in large cargo carriers. Large tankers can carry in excess of 200,000 cubic meters of ballast. Ballasting rates can be as high as 15,000 to 20,000 cubic meters per hour.xe2x80x9d
Current IMO prescribed ballast water management practices, voluntary for the most part now but expected by many to become mandatory in the near future, are largely based upon a process of ballast water exchange. When practiced, ballast water exchange is variously estimated to achieve a level of effectiveness of between 65% and 90% in the exchange of the original ballast water; depending on ship type (tanker, bulk carrier, containership, etc.) and the specific design of a particular vessel. At the same time, no more than 25% of the particulate sediment contained in the ballast water is eliminated. In connection with this, the U.S. Coast Guard and the Smithsonian Environmental Research Center have established a clearinghouse to assess the level of vessel compliance and the value of ballast water exchange practices. However, it is clear that higher level technology needs to be employed to assure shipboard safety, to provide for effective mitigation of biological invasions, and to reduce sediment loading in ballast tanks.
In support of this, and as stated by Kathy Metcalf, Director, Maritime Affairs of the Chamber of Shipping of America, in a submission on the subject to the U.S. Department of Transportation in August 1998, xe2x80x9cIn both the international and domestic initiatives, ballast water exchange is identified as the only currently viable method of management; however, note is made of the need for development of alternative management methods. Ballast water exchange should not be viewed as the final solution due to the safety issues associated with exchange in the open ocean. We believe that, given proper incentives and flexibility for development, alternative management methods will be identified that will permit treatment of ballast water either onboard or ashore and will prove more effective and far safer than physical exchange methods.xe2x80x9d
The present invention is an alternative to ballast water exchange. According to the invention, centrifugal separator technology with advanced UV or chemical biocide technology are used in a practical, cost effective solution to this problem.
The ballast water treatment system of the invention utilizes newly designed separator to separate the components of influent water in a primary treatment stage; certain organisms, sediment, and a small quantity of water will then be discharged back into the source water. The xe2x80x9ccleanxe2x80x9d water processed by the new separator is then be treated by UV or chemical biocides in a secondary system stage, where the xe2x80x9cresidence timexe2x80x9d will be significantly reduced because of pre-cleaning in the primary stage, before being transferred via the vessel""s ballast pump(s) to the ballast tanks.
Use of UV light and non-oxidizing biocides are the two secondary treatments recommended for further consideration by the Great Lakes Ballast Demonstration Project (Parsons 1997). New high intensity UV lights have recently been developed which promise to increase effectiveness against a broader spectrum of organisms and decrease necessary exposure time, which is critical in the high flow-rate systems needed for ballast water intakes.
Examples of machines that can be used to irradiate the pretreated water with UV are available from a number of international manufacturers and distributors of UV systems.
The use of non-oxidizing biocides is also possible, including several proprietary compounds, at least one of which has a half-life of 12-15 hours. This short half-life is essential because it reduces the potential environmental problem of introducing these compounds into the environment when treated ballast water is discharged. In addition, these compounds are highly effective in very small concentrations (parts per million).
U.S. patents which are material to the separator aspect of the present invention are U.S. Pat. Nos. 1,837,191; 2,073,520; 3,591,011; 4,303,526; 4,305,825; 4,478,712; 4,857,175; 4,864,994; 4,980,064; 5,017,288; 5,084,189; 5,104,520; 5,104,541; 5,225,082; 5,466,372; 5,470,465; 5,500,117; 5,510,017; 5,667,686; and 5,858,228.
Accordingly, an object of the present invention is to provide an apparatus for treating water to be supplied to a ballast tank and for reducing silt and sediment build-up in the ballast tank, which comprises: means defining a water pathway having a main inlet for connection to a body of navigable open raw water containing sediment and marine organisms, and a main outlet for connection to a vessel""s ballast tank(s); centrifugal separator means in the pathway and having a separator means inlet for receiving the raw water, the separator means separating sediment with some water from the raw water to produce initially processed water which contains at least some marine organisms, the separator means having a first outlet for supplying the initially processed water to the pathway, and a second outlet for returning the sediment with some water to the body of raw water; biocide means connected to the first outlet and in the pathway downstream of the separator means from the main inlet, for receiving the initially processed water and for disabling the marine organisms in the initially processed water to produce treated ballast water; and ballast pump means connected to the pathway, in line with the biocide means for pumping water along the pathway between the main inlet and the main outlet, and through the separator means and the biocide means.
A further object is to provide such an apparatus wherein the centrifugal separator means can be used as a general purpose separator and which, for general use and for use in the ballast water treatment system, comprises fluid passage means connected between the separator means inlet for receiving the raw water and the first and second outlets, the separator means having a longitudinal axis; a discharge conduit connected to the second outlet; stator means positioned in the fluid passage means for imparting an initial swirling axial movement to the raw water in the fluid passage means passing the stator means; rotatable solid core rotor means positioned in the fluid passage means downstream of the stator means for imparting a further swirling axial movement to the raw water in the fluid passage means downstream of the rotor means and in the discharge conduit and causing the sediment to migrate outwardly; the stator means comprising a stator hub and a plurality of circumferentially spaced fixed helical blades connected to the stator hub, the rotor means comprising an rotor hub and a plurality of circumferentially spaced rotating helical blades connected to the rotor hub.
A still further object of the invention is to provided such an apparatus wherein the biocide means comprises UV irradiation means for killing and/or altering the DNA of the marine organisms by irradiation or wherein the biocide means comprises chemical means for killing and/or altering the DNA of the marine organisms using a chemical biocidal agent.
Another object of the invention is to provide a method for treating water to be supplied to a ballast tank, comprising: establishing a water pathway having a main inlet for connection to a body of navigable open raw water containing sediment and marine organisms, and a main outlet for connection to a vessel""s ballast tank(s); centrifugally separating the raw water for separating sediment with some water from the raw water to produce initially processed water which contains at least some marine organisms, the separating step taking place in the pathway; subjecting the initially processed water to a biocidal action downstream of the centrifugal separating step in the pathway killing and/or altering the DNA of the marine organisms in the initially processed water to produce treated ballast water and pumping water along the pathway using a ballast pump means in line with the biocidal action step.
A further objective of the invention is to provide a method wherein the biocidal step comprises UV irradiation of the marine organisms or exposing the organisms to a chemical biocidal agent.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.